1. Field of the Invention
This invention relates to simple but efficient process for optical resolution of 3-methylamino-4-methylenepyrrolidine derivatives of the formula (I): ##STR2## wherein R is hydrogen or amino-protecting group,
2. Prior Art
The racemic compound (I) mentioned above is known as key material for a certain substituent to be introduced into various pyridonecarboxylic acid-type antibacterials including quinoline-type, naphthyridine-type, pyridopyrimidine-type, and cinnoline-type ones.
For example, pyridonecarboxylic acid type antibacterials possessing 3-methylamino-4-methylenepyrrolidin-1-yl as substituent are disclosed in U.S. Pat. No. 5,017,581. Further, it is confirmed from the recent study by the present inventors that among such quinolone type antibacterials, their (-)-form ones have excellent antibacterial activities with less side-effect. But the optical resolution of the final product is uneconomical because of useless process. Therefore, asymmetric synthesis or optical resolution of this substituent is quite desirable. But asymmetric syntheses usually require long processes and are not practically uneconomic. When known method of optical resolution (Optical Resolution Procedures for Chemical Compounds ed. Paul Newman 1981) is adopted to the compound (I), it is difficult to obtain the pure compound with ease, large quantity, and low-priced because of the low resulution ability, optical impurity, complicated reaction, and unusual and expensive reagent. In case of adapting tartaric acid, usually, a molar ratio of amino compound and tartaric acid is 1:1. But when this method is adapted to the compound (I), the yield is low and the recrystallization is required for several times.